Cycle Detection in Linked Lists

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Your question is Cycle Detection in Linked Lists. Start with the requirements on the right.

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Problem

Given the head of a singly linked list, determine whether the list contains a cycle. A cycle exists if a node can be reached again by continuously following next pointers.

Return True if the linked list has a cycle, otherwise return False.

Formal Specification

Input: head, the head node of a singly linked list. Each node has fields val and next.
Output: A boolean value indicating whether the list contains a cycle.

You must solve the problem without modifying the linked list structure.

Constraints

0 <= number of nodes <= 10^5
-10^5 <= Node.val <= 10^5
pos is -1 or a valid index
Do not modify the linked list

Function Signature

def has_cycle(head):

Your solutionPython 3

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